Light emitting diode backlight module and driving apparatus thereof

Abstract

A LED backlight module including a LED string and a driving apparatus is provided. The driving apparatus comprises a sensing resistor, an adjustable voltage-divider circuit, a comparator, a power converter and a control circuit. The sensing resistor is coupled between a cathode of the LED string and a ground potential and generates a feedback voltage. The adjustable voltage-divider circuit generates a reference voltage according to a dividing ratio which is controlled by a first signal set and a second signal set. The comparator compares the feedback voltage and the reference voltage, and generates a control signal accordingly. The power converter provides a DC voltage to an anode of the LED string according to the control signal. The control circuit counts a disable period of a dimming signal to generate the first signal set, and counts an enable period of the dimming signal to generate the second signal set.

What is claimed is: 
     
       1. A light emitting diode (LED) driving apparatus, adapted to drive at least one LED string, the LED driving apparatus comprising:
 a sensing resistor, having a first terminal coupled to a cathode of the at least one LED string to generate a feedback voltage and a second terminal coupled to a ground potential; 
 an adjustable voltage-divider circuit, configured to generate a reference voltage according to a dividing ratio, wherein the dividing ratio of the adjustable voltage-divider circuit is controlled by a first signal set and a second signal set; 
 a comparator, having a first input terminal coupled to the first terminal of the sensing resistor to receive the feedback voltage, a second input terminal coupled to the adjustable voltage-divider circuit to receive the reference voltage and an output terminal configured to generate a control signal; 
 a power converter, coupled between the output terminal of the comparator and an anode of the at least one LED string and configured to provide a DC voltage to the anode of the at least one LED string according to the control signal; and 
 a control circuit, coupled to the adjustable voltage-divider circuit and configured to receive a dimming signal, 
 wherein the control circuit counts a disable period of the dimming signal to generate the first signal set and counts an enable period of the dimming signal to generate the second signal set. 
 
     
     
       2. The LED driving apparatus according to  claim 1 , wherein the adjustable voltage-divider circuit comprises:
 a first controllable resistor, having a first terminal coupled to a power potential and a second terminal coupled to a first node; and 
 a second controllable resistor, having a first terminal coupled to the first node to generate the reference voltage and a second terminal coupled to the ground potential, 
 wherein the first controllable resistor is controlled by the first signal set to adjust a resistance of the first controllable resistor, and the second controllable resistor is controlled by the second signal set to adjust a resistance of the second controllable resistor. 
 
     
     
       3. The LED driving apparatus according to  claim 2 , wherein an equivalent resistance of the first controllable resistor is positively correlated to a length of the disable period of the dimming signal, and an equivalent resistance of the second controllable resistor is positively correlated to a length of the enable period of the dimming signal. 
     
     
       4. The LED driving apparatus according to  claim 2 , wherein the first controllable resistor comprises:
 a plurality of switching resistor modules, sequentially connected in series, wherein a first-stage switching resistor module among the switching resistor modules is coupled to the power potential, a last-stage switching resistor module among the switching resistor modules is coupled to the first node, and each of the switching resistor modules is controlled by at least one corresponding signal in the first signal set to change the resistance of the first controllable resistor. 
 
     
     
       5. The LED driving apparatus according to  claim 4 , wherein each of the switching resistor modules comprises:
 a resistor module; and 
 a switch module, connected in parallel to the resistor module and controlled by the at least one corresponding signal in the first signal set to determine a resistance of the switching resistor module. 
 
     
     
       6. The LED driving apparatus according to  claim 5 , wherein
 the resistor module comprises one or more resistors sequentially connected in series or connected in parallel with one another; and 
 the switch module comprises one or more switches sequentially connected in series, and the switches are turned on/turned off respectively according to the at least one corresponding signal in the first signal set. 
 
     
     
       7. The LED driving apparatus according to  claim 2 , wherein the second controllable resistor comprises:
 a plurality of switching resistor modules, sequentially connected in series, wherein a first-stage switching resistor module among the switching resistor modules is coupled to the first node, and a last-stage switching resistor module among the switching resistor modules is coupled to the ground potential, and each of the switching resistor modules is controlled by at least one corresponding signal in the second signal set to change the resistance of the second controllable resistor. 
 
     
     
       8. The LED driving apparatus according to  claim 7 , wherein each of the switching resistor modules comprises:
 a resistor module; and 
 a switch module, connected in parallel with the resistor module and controlled by the at least one corresponding signal in the second signal set to determine the resistance of the switching resistor module. 
 
     
     
       9. The LED driving apparatus according to  claim 8 , wherein
 the resistor module comprises one or more resistors sequentially connected in series or connected in parallel with one another; and 
 the switch module comprises one or more switches sequentially connected in series, and the switches are turned on/turned off respectively according to the at least one corresponding signal in the second signal set. 
 
     
     
       10. The LED driving apparatus according to  claim 1 , wherein the control circuit comprises:
 an edge detecting circuit, configured to receive the dimming signal and detect a rising edge and a falling edge of the dimming signal to generate a reset signal; 
 a counter, configured to receive an input clock signal and coupled to the edge detecting circuit to receive the reset signal, wherein the counter generates a count value in response to the input clock signal and resets the count value in response to the reset signal; and 
 a sampling circuit, configured to receive the dimming signal and coupled to the counter to receive the count value, wherein the sampling circuit samples the count value according to the falling edge of the dimming signal to serve as the second signal set and samples the count value according to the rising edge of the dimming signal to serve as the first signal set. 
 
     
     
       11. An LED backlight module, comprising:
 at least one LED string; and 
 a driving apparatus, coupled to the at least one LED string to drive the at least one LED string, wherein the driving apparatus comprises:
 a sensing resistor, having a first terminal couple to a cathode of the at least one LED string to generate a feedback voltage and a second terminal coupled to a ground potential; 
 an adjustable voltage-divider circuit, configured to generate a reference voltage according to a dividing ratio, wherein the dividing ratio of the adjustable voltage-divider circuit is controlled by a first signal set and a second signal set; 
 a comparator, having a first input terminal coupled to the first terminal of the sensing resistor to receive the feedback voltage, a second input terminal coupled to the adjustable voltage-divider circuit to receive the reference voltage and an output terminal configured to generate a control signal; 
 a power converter, coupled between the output terminal of the comparator and an anode of the at least one LED string and configured to provide a DC voltage to the anode of the at least one LED string according to the control signal; and 
 a control circuit, coupled to the adjustable voltage-divider circuit and configured to receive a dimming signal, 
 wherein the control circuit counts a disable period of the dimming signal to generate the first signal set and counts an enable period of the dimming signal to generate the second signal set. 
 
 
     
     
       12. The LED backlight module according to  claim 11 , wherein the adjustable voltage-divider circuit comprises:
 a first controllable resistor, having a first terminal coupled to a power potential and a second terminal coupled to a first node; and 
 a second controllable resistor, having a first terminal coupled to the first node to generate the reference voltage and a second terminal coupled to the ground potential, 
 wherein the first controllable resistor is controlled by the first signal set to adjust a resistance of the first controllable resistor, and the second controllable resistor is controlled by the second signal set to adjust a resistance of the second controllable resistor. 
 
     
     
       13. The LED backlight module according to  claim 12 , wherein an equivalent resistance of the first controllable resistor is positively correlated to a length of the disable period of the dimming signal, and an equivalent resistance of the second controllable resistor is positively correlated to a length of the enable period of the dimming signal. 
     
     
       14. The LED backlight module according to  claim 12 , wherein the first controllable resistor comprises:
 a plurality of switching resistor modules, sequentially connected in series, wherein a first-stage switching resistor module among the switching resistor modules is coupled to the power potential, and a last-stage switching resistor module among the switching resistor modules is coupled to the first node, and each of the switching resistor modules is controlled by at least one corresponding signal in the first signal set to change the resistance of the first controllable resistor. 
 
     
     
       15. The LED backlight module according to  claim 14 , wherein each of the switching resistor modules comprises:
 a resistor module; and 
 a switch module, connected in parallel to the resistor module and controlled by the at least one corresponding signal in the first signal set to determine a resistance of the switching resistor module. 
 
     
     
       16. The LED backlight module according to  claim 12 , wherein the second controllable resistor comprises:
 a plurality of switching resistor modules, sequentially connected in series, wherein a first-stage switching resistor module among the switching resistor modules is coupled to the first node, and a last-stage switching resistor module among the switching resistor modules is coupled to the ground potential, and each of the switching resistor modules is controlled by at least one corresponding signal in the second signal set to change the resistance of the second controllable resistor. 
 
     
     
       17. The LED backlight module according to  claim 16 , wherein each of the switching resistor modules comprises:
 a resistor module; and 
 a switch module, connected in parallel with the resistor module and controlled by the at least one corresponding signal in the second signal set to determine the resistance of the switching resistor module. 
 
     
     
       18. The LED backlight module according to  claim 11 , wherein the control circuit comprises:
 an edge detecting circuit, configured to receive the dimming signal and detect a rising edge and a falling edge of the dimming signal to generate a reset signal; 
 a counter, configured to receive an input clock signal and coupled to the edge detecting circuit to receive the reset signal, wherein the counter generates a count value in response to the input clock signal and resets the count value in response to the reset signal; and 
 a sampling circuit, configured to receive the dimming signal and coupled to the counter to receive the count value, wherein the sampling circuit samples the count value according to the falling edge of the dimming signal to serve as the second signal set and samples the count value according to the rising edge of the dimming signal to serve as the first signal set.